The Histology and Comparative Pathology (Core C) will provide the four projects of this U19 CMCR grant a comprehensive histopathology facility that will assist the investigators in the histological analysis required for the investigators to analyze the role of stem cells in improving the outcome of radiation induce gastrointestinal syndrome (RIGS), Radiation induced hematopoietic syndrome (RIHS), and Radiation-induced cutaneous syndrome (RICS). The core will provide advice on preparafion and processing of samples, as well as on the techniques and procedures available for the different studies. The Core will provide necropsy and histopathology services for phenotypic analysis along with a full range of histological services The services offered by the core will include: protocol design, necropsy, including tissue fixation, tissue proceeding to paraffin block, frozen embedding, standard and specialized stains and immunohistochemieal analyses. It will also include histopathological evaluafion of tissue samples utilizing a standardized method of analysis. The kev personnel of the core will be the director and the histology technical staff. The director will be responsible for supervising all the activities of the core, offering advice on the different methods and procedures, interpretafion of the results, and generating histopathology reports and interpretations of the data. The technical staff will prepare and process tissue samples as appropriate for the study at hand, perform some of the specialized techniques and procedures (e.g. immunohistochemistry and special stains). Significance: Appropriate tissue sample preparation (fixation, processing, trimming and staining) is essential to all projects in this Program Project as it allow the study of the in vivo impact of stem cell technologies on the outcome of radiation-induced injury.